This invention relates to absorption refrigeration systems; and more particularly to absorption refrigeration systems driven by relatively low temperature sensible waste heat sources.
Absorption refrigeration systems are heat operated cycles in which a secondary fluid, termed the absorbent, is employed to absorb the primary fluid, termed refrigerant, which has been vaporized in an evaporator. The combination of the absorbent and refrigerant is termed the working solution. Such systems are thermally motivated, with a source of heat energy being supplied to one thermodynamic cycle (heat engine) at a useful temperature so that, in rejecting a portion of that heat energy to an ambient sink, work in the form of a vapor pressure difference in the refrigerant is generated. This vapor pressure difference is the work input to a second thermodynamic cycle (Rankine cycle) that transfers heat from an external source to the cold evaporator producing the refrigerating effect. Except for a small direct mechanical input to solution and circulating pumps, all energy to drive the system is derived from the heat energy source.
Simple absorption cycle refrigeration systems are able to operate with a coefficient of performance (COP) of about 0.7, where EQU COP=[T.sub.l (T.sub.h -T.sub.s)]/[T.sub.h (T.sub.s -T.sub.l)]
and T.sub.l is the temperature of the refrigeration load, T.sub.h is the temperature of the heat source, and T.sub.s is the temperature of the ambient heat sink, all in degrees Rankine. However, recent rises in fuel costs have led to the need for the use of multiple effect cycles in absorption refrigeration systems which increase the energy efficiency of such systems and raise the COP of such systems to values above 1.0. In such multiple effect cycles, two or more generators (desorbers) are employed, one being driven by high quality heat from an external source with the other generator or generators being driven by the heat of condensation of the refrigerant vapor from the first generator. Condensate from these generators is conveyed to the evaporator. The coefficient of performance is increased by about 50% for each multiple-effect cycle.
In order to lower fuel costs, not only is there a need for improved energy efficiency, but it is also desirable to improve energy utilization of heretofore wasted sources of low grade heat. These sources include heat provided as a by-products of a chemical reaction or available as heat losses from boilers, drying equipment, chemical reactors, or the like. It has been suggested that such heretofore waste heat be used instead of higher grade energy sources to provide the energy requirements for absorption refrigeration cycle comfort conditioning for commercial and industrial facilities.
However, much of the available waste heat from the above-mentioned sources is at a temperature too low to be readily usable in absorption cooling systems. For example, a simple absorption cycle system provides no cooling from heat sources having a temperature of 170.degree. F. or below. But, many industrial process waste heat streams are available at 130.degree.-150.degree. F.
Accordingly, the need exists for an absorption refrigeration cycle system which can utilize the low grade sensible heat available from industrial process streams either for comfort conditioning, self-cooling of such process streams, or other uses.